1981 Lincoln Continental Mark 6 what type of AC refrigerant do I use R12 or r134?

Back in 81 it was R12 but the vehicle could have been retrofitted to take 134A, the best way to tell is look at the low and high side pressure ports, if it looks like they have had little fittings placed over the stock ones then it has been retrofitted to 134A if there are no caps then it is still R12.

If it is still R12, I would have it changed over to R134a. R134a is much cheaper, readily available and environmentally friendly.

Hi tennisshoes, Thanks for your answer sorry I'm so late getting back to you I don't drive the car everyday here's a photo of the ports that you were talking about they do have smaller plastic caps on them but I don't know if they are 134a is there any way you can look at the photo and let me know is it 134a or is it still an R12 AC system? Now on the filter drier it had a label that said made in China so I'm assuming it's at least been maintained or has been redone to 134a but I don't know maybe you can help me out preciate it mister tennisshoes thanks again kind sir!

Sorry here's the photo of the recharging ports with the caps on them hopefully this is a 134a system please if you can let me know?

That’s an old R12 port, so most likely it has never been refitted for 134A. You maybe able to find some R12 sometimes but it is very expensive. It would be best to have it refitted to 134A, have your favorite shop do it so you know it has been done right so you don’t blow a compressor and really mess up the system.